Coital Exanthema in Horses

By PetMD Editorial on Nov. 10, 2011

Genital Horse Pox

Sometimes referred to as genital horse pox, equine coital exanthema is a sexually transmissible disease in horses caused by a herpes virus. Typically, this disease is transferred from horse to horse through sexual contact, but it can also be transferred through unsanitary medical practices, such as when a veterinarian examines multiple horses without changing the examination gloves or instruments between patients. It is for this reason that even horses that have not yet been bred can acquire the virus.

Response is based on the symptoms and relieving the horse's discomfort as much as possible. While there is no treatment, the equine herpes virus does not affect the horse's ability to reproduce, but you will need to be aware of viral outbreaks so that you can prevent your horse from spreading the virus to other horses.

Symptoms and Types

There are several symptoms associated with coital exanthema that may pass unnoticed. The horse may have a slight fever, or the lesions associated with the virus may be small and partially hidden within the folds of the vulval skin. Other symptoms can be indicative of a severe problem, such as reluctance to copulate or obvious discomfort. Typically, symptoms appear within 4-8 days of sexual contact or since a vaginal or rectal examination was performed. Some additional symptoms that may include:

  • Nodular or pustular lumps around the vaginal area in females (mares), including the perineum, the clitoris, or the inner or outer labia
  • Nodular or pustular lumps around the penis in males (stallions), including the perineum and prepuce
  • Fluid-filled vesicles (small blisters)
  • Inflammation of the genital area
  • Soreness
  • Shallow ulcers
  • Vaginal discharge
  • Reluctance to engage in breeding activity
  • Ulcers or pustules may be seen on the lips and nose or teats as well


  • Equine herpes virus type 3.  This virus is spread by:
    • Sexual contact with an infected horse
    • Unsanitary medical practices – not sterilizing instruments between genital or rectal examinations, not changing examination gloves between patients


You will need to give a thorough history of your horse's health and recent activities, such as whether your horse has had contact with other horses, has been recently bred, or has had an examination performed by another doctor. Many times, the presence of vesicles on the genitalia is enough for your veterinarian to form a tentative diagnosis. Only cell analysis of the viral sample will confirm the initial diagnosis.


In most cases of coital exanthema, if no secondary bacterial infection is present, lesions generally last less than two weeks from the day the first lesion appeared, fully healing in three weeks. There may remain residual scars or dark spots on the skin where the ulcers were found, but once the ulcers have healed over, your horse will no longer be contagious to other horses and can be safely bred.

In more severe cases, slightly more extreme measures may be taken as far as treatment is concerned, but only to treat the symptoms – that is, to relieve your horse's discomfort – or to prevent secondary complications from occurring. Oral antibiotics, topical antibiotic creams, or basic antiseptic ointment for relieving pain and itching may be prescribed for the duration of the symptoms. This may help to control some of the pain.

Living and Management

The most important thing to remember when it comes to equine coital exanthema is that a period of isolation and sexual rest is necessary to allow the viral infection to clear up in a timely manner. Allowing mares and stallions to engage in sexual activity while lesions are still present will delay the healing of the infection and creates the risk of spreading it further, as well as increasing the risk of secondary bacterial infection. During the period in which the horse is infectious, disposable instruments and examining materials should be used, with extra attention given to sterilizing the immediate environment.

If it is the case that your mare needs to be impregnated at a time when she is having an outbreak of the virus, you will need to consult with your veterinarian about other techniques for impregnation, such as artificial insemination.  Past infections with coital exanthema will not compromise a mare’s ability to conceive and carry a foal.


There is no vaccine available for equine coital exanthema. It is the responsibility of the breeder or horse owner to properly inspect their mares and stallions to ensure that they are fit for breeding. If one or both of the horses are found to be unfit for breeding due to coital exanthema, a period of sexual rest should be allowed to give the infection time to clear up, during which time an antibiotic or antiseptic treatment can be used to increase the healing time and protect your horse from secondary infections.

The best chance of protecting your horse from coital exanthema is to insist on veterinary and visual examinations before allowing your horse to be bred with an otherwise unfamiliar horse, and to insist that your veterinarian use sterilized instruments and new or unused disposable gloves before vaginal and/or rectal exams on your horse.

To prevent your horse from spreading the disease to other horses you will need to isolate your horse during the time it has active lesions, until the lesions have healed entirely – about three weeks or less.

Help us make PetMD better

Was this article helpful?

Get Instant Vet Help Via Chat or Video. Connect with a Vet. Chewy Health